Porcelain Tile Installation for Dome of Chapel of St. Mary's College

Orinda, Vallejo
California, USA

The dome of St. Mary's Chapel had multiple sources of decay, beginning with seismic damage, which allowed moisture to seep into the interior and delaminate the dome structurally. Stabilizing the concrete underpinning was required before new solid-body porcelain tile installation, to match the original decorative surface design, but in the new much more durable material.

We recrafted the medallions offsite. Using full scale drawings, we were able to reproduce the design elements in reverse, setting each tessera in a water-soluble adhesive on top of the pattern, and segmented for easier installation. These paper-backed design motifs were then transferred to the job site for final installation on each of six faces on the dome, using thin-set adhesive. The water-based glue keeping the paper pattern in place could then be removed by soaking in water and rinsing with pressurized water. Once all tiles were installed, the medallions were rinsed with water to loosen the water-based glue residue, and the paper and residue removed. Grouting could then take place on the entire dome to complete the restoration.

Special scaffolding access was required to complete the strengthening and restoration of the clocktower dome above the campus chapel.

After selective removal of the original failed terra cotta tile and setting bed substrate, the cast-in-place concrete substrate was prepared by attaching stainless steel mesh in pre-divided octagonal sections.

Removable PVC 'ribs' allowed us to segment the dome and install new base material similar to the original construction.

After each segment of polymer-modified setting bed mortar was installed, it was covered with burlap and kept moist for 72 hours to improve the cure-related strength properties of the mortar. This attention to detail in the installation of new mortars is crucial in ensuring the long-term stability of the entire installation.

The architect had decided to replace the original terra cotta tile surface with a more durable medium, solid-body porcelain tile. The original design was scrupulously replicated, but the ceramic medium was improved to a much more durable material.

Using full scale drawings, we were able to reproduce the design elements in reverse, setting each tessera in a water-soluble adhesive on top of the pattern, and segmented for easier installation.

A tight schedule mandated simultaneous activites at the site as well as at the studio. While medallions were crafted off-site, the infill tile work was progressing on the newly-stabilized dome.

These paper-backed design motifs were then transferred to the job site for final installation on each of six faces on the dome, using thin-set adhesive.

Final infill work around each installed medallion was completed and the whole installation grouted.

The water-based glue keeping the paper pattern in place could then be removed by soaking in water and rinsing with pressurized water.

Final tile installation in the cupola area of the dome completed the replacement process.

Once all tiles were installed, the medallions were rinsed with water to loosen the water-based glue residue, and the paper and residue removed. Grouting could then take place on the entire dome to complete the restoration.

The resulting installation will be much more durable over the years.

As long as the concrete substrate remains stable, this installation will be a viable decorative surface indefinitely.

The dome at St. Mary's Chapel is set to provide a picturesque background for another hundred years of wedding pictures.